1. Field of the Invention
The present invention relates in general to an automatic focusing mechanism of a camera, and more particularly to an automatic focusing device having a close-up focal control for focusing a subject which is closer than the short range shooting limit of the camera lens.
2. Prior Art
There are various types of automatic focusing mechanism in cameras. Of those, the systems used commonly and frequently are the types using the principles of triangulation. These systems set the camera lens at the focal point by receiving the light from the subject directly to a range finder or by projecting the flux of light to the subject from the range finder and then by receiving the reflected light from the subject by the above mentioned range finder.
Another system, that does not depend on the principles of trigonometrical survey, sets the lens at the focal point by focusing light from the subject into an image at C.C.D. through a single light receiving lens, etc., and then by detecting the space phase difference.
For any of the cameras provided with the automatic focusing devices as mentioned above, it is impossible to take a picture of the subject that is closer than the short range shooting limit set for the camera lens, due to the restrictions imposed on the camera, such as the helicoid of the camera lens, etc. Therefore, such cameras did not have the close-up range finding-focusing functions.
As mentioned above, the cameras provided with the conventional type automatic focusing devices have the disadvantage that it is impossible to take photographs of the subject extremely close and exceeds the short range shooting limit.